Storage tube



A. S. JENSEN STORAGE TUBE Nov. 13, 1956 ORNEY STORAGE TUBE ArthurSeigfried Jensen, Princeton, N. J., assignor to Radio Corporation ofAmerica, a corporation of Dela- Ware Application April 1, 1952, SerialNo. 279,851

12 Claims. (Cl. 313-68) This invention is directed to an electrondischarge tube, and more specifically to a storage tube having adielectric target upon which a charge pattern may be established andused to provide output signals from the tube.

One type of storage tube is tha-t similar to the tube disclosed in U. S.Patent 2,548,405 to R. L. Snyder, Jr. Such a storage tube consists of anelectron gun for producing an electron beam along a path. Mountedtransversely to the beam path is a target electrode consisting of aninsulating lm having a dielectric surface facing the electron gun and aconductive coating or signal plate spanning the other surface of theinsulating film. Mounted closely adjacent to and overlying thedielectric surface is a tine mesh screen. During tube operation the linemesh screen is maintained negatively to the potential of the conductivetarget coating or signal plate. The electron beam is scanned over thedielectric surface of the target electrode and simultaneously incomingsignal pulses are applied to the signal plate of the target. Theseincoming signals swing the potential of the target signal plate relativeto the negative potential of the fine mesh screen. The secondaryemission initiated by the electron beam from the dielectric surface isthus varied in accordance with the incoming signals. The negative screendrives the secondary emission back to each elemental area of thedielectric target surface and thus each elemental area becomesnegatively charged to an amount corresponding to the signal applied tothe signal plate at that moment. This produces on the dielectric targetsurface a charge pattern corresponding to both the beam scansion and theincoming signals applied to the target signal plate. Upon furtherscansion of the dielectric surface by the electron beam, the secondaryelectron emission initiatedby the beam is directed to a collectorelectrode Within the tube to provide the video or output signal of thetube.

Such storage tubes, as described above, have many applications. in highfrequency work, in which high frequency signals are fed to the tube. Forexample, such applications may be those involving computers or signalamplitude analysis. In such applications, it is possible to apply thehigh frequency signals to the control grid of the electron gun. Also, itis desirable to use electrostatic deflection provided by two pairs ofdeflection plates mounted between the electron gun and the target. Withelectrostatic deflection of this type, it is possible to use higherdeection frequencies.

For high frequency applications, however, storage tubes of the typedescribed, have several disadvantages. For example, the signal providedby the collection of the secondary electrons from the target electrodeis relatively small. Furthermore, the deflection frequencies applied tothe electrostatic deection plates can not be satisfactorily shieldedfrom the collector or output signal electrode which is mounted betweenthe deflection plates and the target. Even when the barrier grid isgrounded, or by-passed to ground to provide shielding between thedeection frequencies and the target signal plate, there tates l. atentIt is particularly desirable to use such tubes Aice is too muchcapacitance between the signal plate and the barrier grid of the targetfor the simple design of an output video amplifier, for example. Anotherdisadvantage of using such a tube with high frequency signals is thatwhen the high frequency input signal is applied to the control grid ofthe gun of the tube, the signals used are radiated to the other tubeelectrodes including the output or collector electrode between the gunand the target. For high frequency work it is desirable, if notnecessary, that the input and output sections of the tube be entirelyseparated so that there will be no interaction between these electrodes.

It is, therefore, an object of my invention to provide a storage tube inwhich the output electrode of the tube is not affected by the inputsignal or the deection frequencies of the tube.

It is a further object of my invention to provide an electron storagetube in which the output and input electrodes are electrically separatedfrom each other.

It is another object of my invention to provide an electron storage tubefor high frequency operation in which the output portion of the tube iscompletely shielded electrically from the input portion of the tube.

Specifically, the invention is directed to a storage tube having adielectric target and a barrier grid immediately adjacent the targetsurface. A charge pattern is established on the surface of the target byscanning the target with a modulated electron beam. The output signalsof the tube are provided by changing the modulated electron beam to anunmodulated beam and scanning the charged surface of the target. Thetarget signal plate which is capacitively coupled to the dielectricsurface provides means for inducing output signals from the tube.Between the target and the electron gun there is provided shieldingmeans to electrically separate the input signals fed to the gun from theoutput signals induced by scanning the dielectric target surface withthe unmodulated electron beam.

Figure l discloses a sectional View of a storage tube in accordance withthe invention.

Figure 2 is a partial sectional view of a modification of the invention.

Figure l shows an electron storage tube having a vitreous envelope 10including an electron gun 12 mounted at one end of the envelope. Theelectron gun is to provide an electron beam along a path 14 extendingsubstantially coaxially with the tubular envelope. Mounted at the otherend of the tubular envelope 10 is a target electrode 16 arrangedtransversely to the beam path 14. The electron gun consists somewhat ofconventional parts and comprises a cathode electrode 18, which may be ashort tubular member having a closed end facing the target electrode 16.Enclosing cathode electrode 18 is a tubular control grid electrode 20coaxially mounted with respect to cathode 18. Arranged substantiallyalong the tube axis and spaced from each other are successively a rstaccelerating electrode 22, a decelerating plate electrode 24 and asecond accelerating plate electrode 26. Each of the electrodes 20, 22,24 and 26 have apertured openings therethrough substantially on the tubeaxis to provide passage therethrough of electrons from cathode 18. Theseelectrons are formed into a beam by the several gun electrodes anddirected and focussed by gun 12 to a tine point on the surface of target16.

The electron beam passes between a pair of horizontal deecting plates 28and a second pair of vertical deflecting plates 30, to which appropriatepotentials are applied to cause the electron beam to be scanned'in araster over the surface of target 16. The pairs of deiectingV plates 28and 30 are respectively connected to sources 32 and 34, of saw-toothvoltages of any desired type and providing any arbitrary scan such asline and frame scansion of the electron beam over the target surface.For computer Y VBetween the pairs of deec'ting plates 28 and 30 thereYismounted a shield electrode 36. Also, a conductive electrode coating 38is deposited on the inner surface of envelope to formsubstantially atubular electrode enclosing the second accelerating plate electrode 26and the pairs of deilecting plates 28 and 30. `A second tubular wallcoating electrode 39 is spaced'fror'n coating 38 and extends'toV andpartially encloses target 16. The conductive coatings 38 and 39 may beof any appropriate type such as a colloidalV suspension of carbon inabinder, which may be painted on the glass wall surface; or a metal- .liccoating such as silver or aluminum, which can be put down on the glasswall surface by metallic evaporation. Also, electrodes 38 and 39 mayconstitute metal tubes mounted in the same relative positions. Wallcoating 38 is tied conductively to the second accelerating electrode 26which is in turn electrically tied to the iirst accelerating electrode22. Electrode 39 is connected to ground, as shown, by a lead 68 sealedthrough the envelope wall.

The several gun electrodes shown are respectively tied to an appropriatesource of potential which may, for eX- ample, be a voltage divider 4t).Voltage values are given as representative of potentials which have beenused successfully in a tube of the type described during tube operation.However, these values need not be limiting but only illustrative.

The target 16 consists essentially of a heavy metal signal plate 42. Athin dielectric sheet 44.such as mica or an equivalent is mounted on thesurface of signal plate 42 facing the electron gun 12. VSpaced closelyto the surface of the dielectric sheet 44 or mounted in contact theretois a fine mesh metal barrier grid Vscreen'46. Screen,

46 is mounted across a support ring 48 in which the target assembly 16is arranged. An insulating disk 50 spaces signal plate 42 from thesupport ring 48. Signal plate 42 is connected to an external circuitthrough lead means 52, while the barrier grid screen 46 is connectedtothe exterior of the tube by lead means 54 connected directlyV to thesupport ring 48.

In operation of the tube, barrier grid 46 and signal Vplate 42 of thetarget assembly 16 are connected to a circuit such as that schematicallyshown in the igure. Barrier grid 46 is connected by lead 54 to a point57 in the circuit between a high resistance 56 and a pentode tube58,'while signal plate 42, as shown is connected by lead 52 to a point59 between the high resistance 56 and a diode'60, such as a crystaldiode, for example. Point 59 of the circuit is connected directly to thecontrol grid ofa triode 61. As shown, the several terminalspto which thecircuit parts are connected are maintained at appropriate potentials,the values of which are shown in the igure.

During tube operation, the control grid 20 of the electron gun 12 ispulsed above cutoi by the application of a square wave signal 63 througha conductor 64. The time ofthe negative pulse 65 of the square Wavesignal is referred to as the writing time, while the time of thepositive pulse 67 of the square wave signal is referred to as thereading time. Any signal 69 which is to be stored on the target 16 issuperimposed upon the square wave signal during the writing time. Suchsignals are of high frequency and pulse the control grid potential abovecutoff so that the electron beam directed' at target 16 is a modulatedbeam in accordance with the signals applied during the writingtime. Themodulated beamV during this writing time is scanned over thesurfaceofthe dielectric sheet 44. Since the cathode 18 ofthe gun is operated atabout -1200 'volts, and thef barrier grid 46 is operated intheneighborhood of a negative 3Q() volts,

the electron beam will strike the surface of the dielectricY Y sheet;v44 with Vsuicient energy to drive oit more secondary electrons than Vthenumber of primary beam electrons below cutoif. Thus, during the writingtime pentode 58.

conducts and there is a iiow of current through pentode 58 resistor 56,and diode 60. During this time, the Vbarrier grid 46 assumes a negativepotential in the order of 20 volts below that of the signal plate 42.During'the reading` time, current flow through `pentode 58 is cut-off,and with no flow of current across resistance 56, barrier grid screen 46and signal plate 42 assume the same potential. v

During the reading time of tube operation, with signal plate 42 andbarrier grid 46 at the same potential, the electron beam is scanned overthe surface of the dielectric sheet 44 in a complete raster. Thesecondary emission from the dielectric sheet passes out through thebarrier grid 46 and is collected by the Wall coating 39 Vwhich is at amore positive potential. Due to the secondary emission leaving thedielectric surface of sheet 44, this surface will be driven positivelyuntil it reaches an equilibrium potential which is substantially that ofthe 4adjacent grid electrode 46. At this potential sutlicientsecondaries are driven back to the dielectric surfaceto maintain it atequilibrium potential. During the writing cycle of tube operation, theincoming signal V69 is superimposed upon the square wave signal fed tothe control grid 20, as described above. The electron beam is thusmodulated as it is scanned over the surface of the dielectric sheet 44.During this writing time, however, since the barrier grid 46 is now some2i) volts or more negative to its previous value, the secondaryelectrons initiated under beam bombardment are repelled back to thedielectric surface, which is thus driven negatively at eachelementalarea in proportion tothe strength of the beam current strikingthat element. In this manner then, Ias the beam is scanned over thetarget surface during the writing cycle there is established on thedielectric surface of film 44 a succes sion of charges corresponding tothe successive modulations of the electron beam. In this manner, thereis established a charge pattern on the dielectric surface of sheet 44corresponding from point to point successively to the signal pulsessuperimposed-on the square wave appliedV to the control grid 20 duringthe writing time. During the next pulse -or reading time the full beamscanning over the surface of sheet 44 again drives this surfacepositively to the equilibrium potential equal to that of the barriergrid 46. emission from each point of the target surface is nowdetermined by the charge yat that point, which was established by themodulated beam during the writing time. As each elementary area Vof Vthetarget is thus discharged by the full beam, a signal pulse occurs in thecircuit of the target signal plate 42. These signal pulses are eachproportional to the charge which the beam erases from point to point.These signalvpulses are established on fresults in Vspurious signals inthe output circuit of 'the tube. It is desirable that such spurious'signals do not Thus, during the writing However, the secondaryA occurand that there is no electrical coupling between the input and outputsections of the tube.

In accordance with the invention the tube is designed to provideelectric shielding ofthe input and output portions. The invention iscarried out by mounting a conductive screen electrode 66 adjacent thedeecting system of the tube and between gun 12 and the target electrode16. Screen 66 is a large mesh screen of approximately 10 mesh per inch.The screen is mounted on a conductive ring 68 sealed through theenvelope wall 10. As shown in the drawing, ring 68 and screen 66 areconnected directly to ground by a lead 70. Also, in accordance with theinvention, the portion of the tube envelope extending from the ring 68and beyond the target electrode 16 is enclosed in a tubular metalcanister or container 72. This canister 72 may be either connecteddirectly to ground or through ring 68 to ground. This provides agrounded external shield for target electrode 16. Furthermore, container72 is extended beyond the target end of the tube envelope 10. Thisprovides a shielded mounting for the output circuit of the tube which isplaced Within container 72, so that it is effectively shielded from theinput signals applied to the control electrode 2i) of gun 12. Theinternal accelerating electrode coating '39 provides further shieldingbetween the input and output portion of the tube by grounding thecoating through spring iingers 74 mounted on ring 68. Coating 39 extendsbeyond and substantially encloses the target electrode 16. In lieu ofthis coating and the ring seal, this entire end of the tube may be madeof metal with insulating beads through which the barrier grid 54 andplate 52 leads emerge in Well-known fashion.

Such a modification is shown in Figure 2. The gun end of the glassenvelope is sealed directly to a metal cylinder 8i), which forms thetarget end of the tube envelope, as shown. Target 16 is mounted by meansof its leads 52 and 54 on a metal header 82 which is fitted into theopen end of cylinder 80 and sealed thereto. Leads 52 `and 54 are broughtout through apertures in header Si) and are insulated from the header 82by glass beads 84 and 86 sealed into the apertures. Cylinder 80 may beextended farther beyond header 82 to serve as a screening container foroutput circuits in the manner described above for Figure l. Or anadditional metal cylinder may be slipped over the end of cylinder 80 toserve this purpose and in the manner described above for cannister 72.Screen 66 may be fixed across a mounting ring 8S which in turn is weldedto the metal cylinder 80. In this manner the input `and output portionsof the tube are shielded. Cylinder 30 also serves as a collectorelectrode for secondary electrons from target 16 in the manner ofelectrode 39, described above.

The use of the support ring 68 sealed through the envelope Wall providesfor shielding elements 39, 66 and 72, a short lead passing out of thetube envelope. Ring 68 has little capacitive coupling to the input andoutput portions of the tube.

The screen 66, together with the ring 68, and shields 39 and 72,completely separate the input and output portions of the tube. With thisshielding arrangement, the input signals have little or no eiect on theoutput circuit portions of the tube. Furthermore, the high frequencydeflection voltages applied to plates 28 and 30 will in no way eiect thereading and writing functions at target 16. Again, by utilizing such ashielding arrangement, it is unnecessary to depend upon the barrier grid46 as a shield between the input portion of the tube and the signalplate 42. This has proved an advantage since use of barrier grid 46 asan electrostatic shield necessitates tying it to ground potential andunduly increasing the capacity between grid 46 and signal plate 42. 'Iheoutput capacitance of the tube, as modiiied by the invention, is nowonly between the target electrodes 42 and 46 and the shieldingelectrodes 66, 39 and 72, which because of their design and natureprovide a capacitance considerably less than is possible without theiruse. The tube, shown in the figure, has been described above as beingoperative in connection with `a particular form of output circuit. Theoperation of the tube, however, is not limited to this particularcircuit. It has been recognized that certain circuit requirements arenecessary for optimum operation of the tube. If the tube is operatedwith the video input signal applied to the control grid 20 of gun 12, itis desirable for optimum operation that, during Writing, screen 46should be well by-passed to ground `and that the keying signals shouldbe applied to the signal plate 42, so that it is driven positivelyduring writing, and is returned to its normal potential during reading.For this type of operation during the reading time, both the plate 42and the screen 46 must be sepa* rated from ground by a high impedance,and the output reading signal is taken oit the barrier grid.

The tube may also be operated by applying the incoming video signals tothe plate 42 and simultaneously scanning the target with an unmodulatedbeam from the gun 12. The video input signals should be kept to about 20volts maximum for linear operation. During this time the screen 46 iskept at a constant potential negative to that potential to which theplate 42 is driven by the input signals. In this manner, a chargepattern is established on the dielectric sheet 44 by secondary electronsdriven back to the dielectric surface by the negative grid 46. Duringreading both the plate 42 and screen 46 are kept at a common potentialwhile the unmodulated beam is scanned across the target to erase thecharge pattern established thereon. Again the output signal may be takenoir the barrier grid while both barrier grid and plate are separatedfrom ground by a high impedance. This last method of operation issimilar to that described in U. S. Patent 2,548,405 of Snyder.

The tube described above is one which does not require a collectorelectrode to provide the output signal of the tube. Since reading andWriting are sequential and not simultaneous, a collector electrodebetween the gun 12 and the target 16 is unnecessary. The use of such acollector electrode requires excessive shielding electrodes surroundingthe collector which in turn necessitates longer gun-to-target spacing.With the design described above and as shown in the drawing, it ispossible to mount the gun 12 closer to the target 16 and thus provide asmaller spot size of the beam on the target surface and thus betterresolution.

The secondary electrons passing from target sheet 44 through the meshscreen 46 are now enabled to be collected by any more positiveelectrode. There is thus no necessity for directing them speciiically toan output collector electrode with a resulting shading of the outputsignal because of non-uniform collection from all portions of the targetsurface. Since the electrode coating 39, as well as the shielding grid66, are maintained more positive than the target surface during tubeoperation, the secondary electrons may pass to these electrodes withoutany attempt to control their collection.

The output signal of the tube described, is produced by the electronsleaving the target and not by their collection. Thus, merely theprovision of a large off-target positive gradient between the target andelectrodes 39 and 66 is sufficient to provide a good signal. In thismanner then, the complications of former storage tubes have beeneliminated and both the structure and operation of the tube has beengreatly simplified with the above described advantages.

While certain specific embodiments have been illustrated and described,it will be understood that various changes and modifications may be madetherein without departing from the spirit and scope of the invention.

What is claimed is:

1. An electron discharge device comprising, an electron gun forproducing au electron beam along a path,

a target electrode spaced from said gun and mounted transversely to saidpath, means shielding said target electrode from said gun, saidshielding means including a conductive screen mounted across said beampath adjacent to said gun and between said gun and said target electrodeand providing a larger space between said conductive screen and saidtarget electrode than between said conductive screen and said gun, and atubular elec-V trode electrically connected to and extending from saidscreen to said target and enclosing said larger space between saidconductive screen and said target electrode and means electricallyinsulating said shielding means from said target and said electron gun.

2. An electron discharge tube comprising, an envelope, an electron gunwithin said envelope for producing an electron beam along a path, atarget electrode spaced from said gun and mounted within said envelopetransversely to said beam path, means between said gun and said targetfor deecting said beam over said target, means shielding said targetelectrode from said deecting means, said shielding means including aconductive screen mounted adjacent to said gun and within said envelopebetween said deilecting means and said target electrode and providing alarger space between said conductive screen and said target electrodethan between said'conductive screen and said gun, and a tubularconductive member electrically connected to and extending from saidscreen to said target and enclosing said larger space between saidconductive screen and said target electrode and, means electricallyinsulating said shielding means l from said target and said deectingmeans.

3. An electron discharge tube comprising, an envelope, an electron gunwithin said envelope for producing an electron beam along a path, atarget electrode mounted within said envelope transversely to said beambath, and means shielding said target electrode from said gun, saidmeans including a conductive screen mounted within said envelope betweensaid gun and said target electrode, a tubular electrode within saidenvelope electrically connected to said screen and extending from said-screen to and partially enclosing said target electrode and a conductormember electrically connected to said screen and extending over theouter surface of said envelope and enclosing said target electrode, andmeans electrically insulating said shielding means from said target andsaid electron gun.

4. An electron discharge tube comprising, an envelope, an electron gunwithin said envelope for producing an electron beam along a path, atarget electrode mounted within said envelope transversely to said beampath, means shielding said target electrode from said gun, said meansincluding a metal ring sealed through the envelope wall between said gunand said target electrode, a conductive screen mounted within saidenvelope across said ring, a tubular electrode within said envelopeextending from said ring to and partially enclosing said targetelectrode and a tubular conductor mounted on the outer surface of saidenvelope between said screen and said target eleci 5. A storage tubecomprising, an envelope, an elec-` tron gun within said envelope forproducing an electronV beam along a path, a target electrode mountedwithin said envelope transversely to said beam path, means be-Y tweensaid gun and said target for deilecting said beam over said target, andmeans shielding said target electrode from said gun and said beamdeflecting means, said shielding means including a conductive screenmounted within said envelope between said gun and said target electrodeand a tubular electrode extending from said screen to and enclosing saidtarget electrode, said tubular electrode comprising a portion of saidenvelope and having a wall portion closing the end thereof away fromsaid conductive screen, and means electrically insulating saidshielding'means from said fleeting means and said gun. ,Y

6. vAn electron discharge device comprising, an envelope, an electrongun within said envelope for producing an electronbeam along a path, atarget electrode mounted within saidenvelope transversely to said beampath, said target electrode including a dielectric sheet and a screenelectrode closely spaced from the surface of said dielectric sheetfacing said gun, means shielding said target electrode from said gun,said shielding means including a tubular conductive member mountedaround said envelope and enclosing said target and a second screenmounted across one end of said tubular member and in said beam pathbetween said gun and said target electrode, said tubular conductivemember havinga conductive wall portion closing the other end thereof,and a tubular electrode within said envelope extending from said secondscreen and 'enclosing said dielectric target sheet, said second screenbeing of a conductive material.

7. A storage tube comprising, an envelope, an electron gun -within saidenvelope for producing an electron beam along a path, a target electrodemounted within said envelope transversely to said beam path, said targetelectrode including a dielectric sheet and a screen electrode closelyspaced from the surface of said dielectric sheet facing said gun, meansshielding said target electrode from said gun, said shielding meansincluding a second conductive screen lmounted across said beam pathbetween said gunV and said target electrode and a tubular electrodeyextending from said second screen and enclosing said dielectric targetsheet, means including a conductor sealed through said envelope andelectrically connecting said secondscreen Vto said tubular electrode,and-means electrically insulating said shielding means from said targetand said gun. Y

SVA- storage tube comprising, an'envelope, an electron gun within saidenvelope for producing an electron beam along a path, a target electrodemounted within saidy envelope transversely to said beam path, saidtarget electrode including a dielectric sheet and a screen electrodeclosely spaced from the surface of said dielectric sheet facing saidgun, v'means shielding said target electrode from said gun, said meansincluding a metal ring sealed through the envelope'between said gun andsaid target electrode, a conductive second screen mounted within saidenvelope across said ring, a'tubular electrode within said'envelopeelectrically joined to said second screen and extending from `said ringto and partially enclosing said target electrode and a tubular conductormounted on the outer surface of said envelope between said screen andsaid Y target electrode and enclosing said target electrode, meansconnecting together said second screen, tubular electrode and tubularconductor, and means electrically insulating said shielding means fromsaid target and said electron gun.

9. A storage tube comprising, an envelope, an electron gun within saidenvelope for producing an electron beam along a path, a Vtargetelectrode mounted within said envelope transversely to said beam path,said target electrode including a-dielectric sheet and a screenelectrode closely spaced from the surface of said dielectric sheetfacing said gun, means shielding said gun from said target electrode,said means including a second conductive screen mounted across/said beampath between said gun and said target electrode'` and a tubularconductive member electrically joined to said second screen andextending V'from said second screen and lenclosing said targetelectrode, said tubular electrode comprising a portion of said envelope,and means electrically insulating said shielding means from said tar-getand said electron gun.

1 0. An electron discharge tube comprising, an envelope having a tubularmetal portion, an electron gun within said envelope for producing anelectron beam directedalong a path into said tubular metal envelopeportion, a target electrode mounted within said metal entarget said de-kaww/47 velope portion transversely to said beam path, a conductive wallportion closing the end of said tubular metal envelope portion away fromsaid gun, means within said envelope between said gun and said targetfor deiiecting said beam over said target, means shielding said targetelectrode from said gun and said deecting means, said shielding meansincluding a conductive screen mounted across the other end of said metaltubular envelope p0rtion between said target and said beam defiectingmeans, and means electrically insulating said shielding means from saidtarget said gun and said dellecting means.

11. An electron discharge device comprising, an electron gun forproducing an electron beam along a path, a target electrode spaced fromsaid gun and mounted transversely to said beam path, means shieldingsaid target electrode from said gun, said shielding means including aconductive apertured electrode mounted across said beam path adjacent tosaid gun and between said gun and said target electrode and providing alarger space between said conductive apertured electrode and said targetelectrode than between said conductive apertured electrode and said gun,and a tubular electrode electrically connected to and extending fromsaid apertured electrode to said target and enclosing said larger spacebetween said conductive apertured electrode and said target elec- 25trode, and means electrically insulating said shielding means from saidtarget and said electron gun.

12. An electron discharge tube comprising, an envelope,

an electron gun within said envelope for producing an electron beamalong a path, a target electrode mounted within said envelopetransversely to said beam path, and means shielding said targetelectrode from said gun, said means including a conductive aperturedelectrode mounted within said envelope between said gun and said targetelectrode, a tubular electrode within said envelope electricallyconnected to said apertured electrode and eX- tending from saidapertured electrode to and partially enclosing said target electrode,and a conductor member electrically connected to said aperturedelectrode and extending over the outer surface of said envelope andenclosing said target electrode, and means electrically insulating saidshielding means from said target and said electron gun.

References Cited in the le of this patent UNITED STATES PATENTSLindenblad Mar. 28, 1939 Jensen et al Apr. 11, 1950 Haei May 16, 1950OTHER REFERENCES Jensen et al.: Barrier Grid Storage Tube and ItsOperation, reprint from RCA Review, March 1948, vol. IX, No. 1, Fig. 5,page 116.

